Check valves are used in piping systems to allow uni-directional flow of fluids. Reverse or backflow of fluids (back flushing) is prevented by the check valve during normal operation. There are various types of check valve designs including 90 degree swing check valves and 45 degree flexible disc check valves. These valves include discs, shafts, stems, and seals located in some examples in the fluid path of the valve. These valves are used in some examples with fluids, such as wastewater, including viscous sludge, stringy material, wet strength paper products, and other debris that tend to foul the interior components of the valves thereby affecting their performance and requiring the valves to be taken out of the line of service. Swing check valves and flexible check valves are less suitable for applications involving fluids with solids and semi-solids therein (e.g., sludges, fluids with entrained solids such as fibrous or stringy material, brush and the like). The materials within the fluid accumulate and foul the discs and shafts of the valves and accordingly frustrate operation of the discs to fully open and also fully close the valves and prevent backflow. For example, the discs and shafts are prone to accumulate stringy material. As the valve mechanisms become fouled the valves require service and maintenance to remove the fouling materials, which involves the valves to be opened to provide access to internal parts. Such service and maintenance requires the valves be taken out of service and contaminated, offensive wastewater and sludge, located upstream of the valves in the pipeline must be drained and disposed of.
Another type of check valve, ball check valves, addresses these issues by providing a valve ball within the valve body. In a zero flow (backflow shutoff) configuration the valve ball returns to its seated position within a seat in the valve body to substantially prevent the backflow of fluid. During normal operation, the flow of fluid pushes the valve ball (e.g., a valve ball of about 2 inch diameter weighing about 0.5 pounds up to a valve ball of about 24 inch diameter weighing over 400 pounds) out of the seat and the fluid flows around the ball. Alternatively, the valve ball is pushed into a recessed area (e.g., a side track area) of the valve body that substantially opens the passage of the valve entirely to facilitate full flow without interference by the valve ball. Because the valve ball is freely movable within the valve body and has a spherical shape, the solids and semi-solids present in sludges, such as sewage and storm water, easily pass through the valve and are not trapped on mechanical components like the discs and shafts present in swing check valves and flexible disc check valves.
The mechanical components of some example swing check valves and flexible disc check valves do include a mechanical linkage that allows for movement of the discs from a seated shutoff position to a backflow position when backflow through the valves is desired. For instance, when backflushing of a pump or draining of a pipeline is needed, the discs of these valves are moved out of engagement with a disc seat to allow for reverse flow of fluids through the valves. Because ball check valves are freely movable within a valve body, the ball check valve is unsuitable for backflow operation.
One example of a ball check valve that allows for backflow is found in U.S. Pat. No. 187,373. The ball check valve in this example includes a valve seat at a 45 degree angle with respect to the main fluid passage (e.g., the seat extends into the fluid passage) that holds the valve ball therein and provides a discontinuity and obstruction to the main fluid passage. The valve includes a rod that engages with the valve ball to bias the valve ball upwardly along the valve seat (e.g., at the 45 degree angle) and accordingly allow at least partial backflow when desired.